Cap for a pneumatic gun

ABSTRACT

A cap has a body with an opening defined in one end of the body. A floor is formed in the opening and is parallel to an end wall of the body defining the opening. An annular flange perpendicularly extends from the floor in the opening. With a specific mold and a specific process, the cap can be formed with a die casting process without draft allowance. The process for forming the cap is simple and the cost for manufacturing the cap is low.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cap, and more particularly to a cap for a pneumatic gun and without a draft allowance being formed in the cap during the die casting process.

[0003] 2. Description of Related Art

[0004] With reference to FIG. 3, a cap (41) is always mounted on a pneumatic gun (40) to define an air chamber for the piston of the pneumatic gun (40). To achieve a good precision in size, the cap (41) is always formed with the cold chamber method of a die casting process. With reference to FIGS. 4 and 5, a metal mold (50) is used to form the cap (41) and comprises a male portion (51) and a female portion (52). An impression (500) with a shape substantially equal to that of the cap (41) is defined between the portions (51,52). A cylinder (53) is connected to the metal mold (50) to force molten material such as Aluminum into the impression (500) through an injecting passage (502). At least one pin (55) is moveably mounted in the mold (50) to enable ejection of the cap (41) from the mold (50).

[0005] In operation, the molten material is fed into the cylinder (53) through a sprue (531) defined in the cylinder (53) with a shank (60). The molten material is forced into the impression (500) through the injecting passage (502) by the piston (54) to fill the impression(500). The melt liquid will solidify to a cap (41) in accordance with the shape of the impression(500) after a cooling process, and the cap (41) can be released from the separated metal mold (50) by using the pins (55). To conveniently take the cap (41) out from the mold (50), draft allowances are previously set in the impression (500) of the metal mold (50), so that oblique faces will be formed in the cap (41) for the cap (41) to be easily released from the mold (50). The draft allowances can also prevent the surface of the cap (41) being damaged when the cap (41) is released from the mold (50).

[0006] However, after the cap (41) has been formed with the die casting process, the unnecessary portion (420) (as shown in the phantom lines in figures) formed by the draft allowances must be cut off. Thus an additional task must be performed on the cap (41), such that the processes for forming the cap (41) for a pneumatic gun (40) are troublesome and the cost for manufacturing the cap (41) is unnecessarily high.

[0007] To overcome the shortcomings, the present invention tends to provide a cap to mitigate and obviate the aforementioned problems.

SUMMARY OF THE INVENTION

[0008] The main objective of the invention is to provide a cap without draft allowances during the die casting process. The cap has a body with an opening defined in one end of the body. A bottom is formed in the opening and is parallel to an edge of the end of the body defining the opening. The annular flange perpendicularly extends from the bottom in the opening. With a specific mold and a specific process, the cap can be formed with a die casting process without draft allowances. The process for forming the cap is simplified, and the cost for manufacturing the cap is reduced.

[0009] Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a cross sectional side plan view of a cap in accordance with the present invention;

[0011]FIG. 2 is a side plan view in partial cross section of a metal mold for forming the cap in FIG. 1;

[0012]FIG. 3 is a perspective view of a pneumatic gun with a conventional cap;

[0013]FIG. 4 is a side plan view in partial cross section of a metal mold for forming the conventional cap in FIG. 3; and

[0014]FIG. 5 is a side plan view of the conventional cap in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0015] With reference to FIG. 1, a cap (30) for a pneumatic gun in accordance with the present invention comprises a body with a closed first end wall and an open second end wall. An opening is defined in the second end wall of the body and a bottom of the opening is defined by a floor that is parallel to the second end wall of the body. An annular flange (31) perpendicularly extends from the floor in the opening. There is not any draft allowance arranged in the cap (30) as is explained in detail later.

[0016] To form the cap (30) without draft allowances, with reference to FIGS. 1 and 2, a metal mold constructed of a female portion (10), a male portion (20) and a cylinder (11) is provided. An impression (100) with a shape substantially equal to that of the cap (30) is defined between the portions (10,20). Multiple cooling channels (13) are defined in the portions (10,20) and extend around the impression (100). The portions (10,20) are selectively made of SKD 61 alloy tool steel. The hardness of the portions (10,20) is in a range H_(RC) 45 to 50. A heat treatment must be applied to the surface of the portions (10,20) to increase the hardness of the surface of the portions (10,20) to H_(RC) 70 with a depth 0.25 mm (millimeter). The smoothness of the surface of the portion (10,20) is 800μ.

[0017] The cylinder (11) is connected to one of the portions (10,20) and is communicated with the impression(100) through an injecting passage (102). A piston (12) is moveably mounted in the cylinder (11) to force molten material such as Aluminum into the impression (100). The preferred temperature of the molten Aluminum is 650 to 680° C. A sprue (110) is defined in the cylinder (11) for the molten material to be fed into the cylinder (11).

[0018] To inject the molten material into the impression (100), the piston (12) forces the molten material into the injecting passage (102) at a low speed 1.5 m/s (meters per second) firstly to avoid the air of the environment from being sucked into the cylinder (11) through the sprue (110). The molten material is then forced into the impression (100) at a speed 4.5 m/s. The air in the impression (100) will be forced into an air chamber (101) communicating with the impression (100). In practice, the air chamber (101) is connected to an air pump (not shown) to exhaust the air from the impression (100) and the air chamber (101), such that a gas bubbles are not formed in the cap (30). The pressure provided by the piston (12) to the molten material is increased to 220 kg/cm² so that the density of the molten material is increased. The molten material is cooled to 180 to 200° C. by cool water passing along the cooling channels (13), whereafter the molten material solidifies as the cap (30) in 20 to 25 seconds, and the melt liquid solidifies to a cap (30). When the cap (30) has cooled its volume is smaller than that in its hot state and a gap is defined between the cap (30) and the inner surface of the impression (100) due to the contraction of the cap (30). The gap can help the cap (30) to be released from the mold without draft allowance. The cap (30) can be directly mounted on a pneumatic gun without any additional tasks being performed on it. Accordingly, the process for manufacturing the cap (30) is simple and the cost for manufacturing the cap (30) is low. In addition, multiple pins (21) are mounted in the mold to eject the cap (30) from the mold.

[0019] In addition, to improve the convenience of releasing the cap (30) from the mold, an isolating agent is previously sprayed onto the inner surface of the impression (100) before the die casting process is undertaken. The agent is a mixture of 10% ester, 4% vegetable oil, 6% silicon oil, 1% polymer and 79% water. The agent is diluted with water at a ratio 1:120 when the agent is used.

[0020] Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A cap for a pneumatic gun comprising: a body having a closed first end wall and an open second end wall; an opening defined in the second end wall of the body and a floor defining a bottom of the opening, the floor being parallel to the second end wall of the body; and an annular flange perpendicularly extending from the floor in the opening, wherein the cap is without any draft allowance during a die casting process for manufacturing the cap. 